Pulses of various lengths (the information itself) will be sent at regular intervals (the carrier frequency of the modulation).
_ _ _ _ _ _ _ _ | | | | | | | | | | | | | | | | Clock | | | | | | | | | | | | | | | | __| |____| |____| |____| |____| |____| |____| |____| |____
_ __ ____ ____ _ Data | | | | | | | | | | | | | | | | | | | | _________| |____| |___| |________| |_| |___________
Data 0 1 2 4 0 4 1 0The clock signal is not necessary as the leading edge of the data signal can be used as the clock if a small offset is added to the data value in order to avoid the lack of a pulse for zero values.
PWM is also used to vary the total amount of power delivered to a load without resistive waste. An RC filter can be used to smooth the pulse train into a steady analog voltage. This method is commonly used in DC motor speed control.
See also: Modulation, Pulse-code modulation, Pulse-amplitude modulation, Pulse-position modulation